No it wasn’t. Under both the Northern proposed New Jersey Plan as well as the Southern proposed Virginia Plan, the President would have actually been elected by Congress. There were concerns that having Congress elect the President would jeopardize separation of powers. So the Electoral College was created, with one elector for each member of Congress. It had nothing to do with protecting the interests of slave-holding states, but instead was designed to make the Presidency more independent of Congress. The fact that the President would be elected by States as opposed to people directly was uncontroversial. What was controversial was whether the apportionment of those votes should be proportional to the population (where both chambers of Congress had proportional votes) or whether it should be the degressive proportionality that we have today (where the upper house has equal representation). The slave-states wanted the former, not the latter, owing to their population advantage.

Also, degressive proportionality as a concept is fairly uncontroversial in the context of Federal electoral systems: https://en.wikipedia.org/wiki/Degressive_proportionality

It’s what’s used to allocate seats in the European Parliament, who vote to elect the President of the European Commission, who is the Head of Government of the EU. In many ways, the structure of the EU is identical to that of the US, especially prior to the passage of the 17th Amendment.